As is commonly known, conventional band saw apparatus include a base fixture on which workpieces to be cut are placed and a saw head assembly which houses a flexible continuous loop saw blade. The band saw blade is mounted around a pair of wheels or pulleys, one of which is driven. Typically, two or more blade guide assemblies are mounted to the head assembly between the wheels or pulleys, which guide assemblies slidably engage the saw blade to orient it in a generally vertical cutting orientation. The section of the saw blade intermediate the saw blade guide assemblies is called the "cutting stretch." The saw blade and the workpiece are displaced relative to one another so that the saw blade contacts and cuts the workpiece at the saw blade cutting stretch. More advanced band saw apparatus head assemblies are so arranged as to be lowered and raised toward and away from the base by a suitable means, such as a hydraulic motor or pneumatically. Movement of the head assembly is often achieved by either being pivotal around a hinge pin or translational along appropriate vertical or horizontal guide posts. Thus, in cutting operations, the saw head assembly is moved toward the base so as to enable the driven band saw blade to cut the workpiece which has been placed on the base.
In recent years, considerable effort has been directed toward enhancing the cutting efficiency and precision of band saws when cutting hard metallic workpieces or the like. One problem often encountered with conventional band saw apparatus is lateral blade deviation from the desired line of cut. Such deviations of the band saw blade adversely affect cutting precision and accuracy, which in extreme cases necessitate scrapping of the workpiece. In other instances, excessive materials are wasted because cutting imprecision is allowed for by increasing the workpiece length. For example, when a square end is desired, the material length of the workpiece will purposely be increased so that the crooked end may be milled or machined down to the proper shape and size. Furthermore, such deviation can result in excessive wear and stress on the blade, thereby, shortening the expectancy of blade life. Ultimately, manufacturing costs are substantially increased.
As stated, two or more movable blade guide assemblies are employed intermediate the blade drive and idler wheels. Generally, the guide assemblies are situated as close as possible to the edges of the workpiece to laterally stabilize the blade against transverse deflection as it cuts through the workpiece. Still, for difficult to cut metals and/or high feed rates, the blade may tend to wonder or move laterally from the desired or nominal line of cut to be made on the workpiece. Factors, such as uneven blade sharpness, also adversely affect blade deviation. Thus, operator knowledge of even the slightest deflection of the blade during operation is quite beneficial in avoiding the rejection of parts and permitting operational adjustments to compensate for deviation.
Since most lateral deviations of the band saw blade cannot be readily noticed by operators during cutting operations, the cutting imprecision will not detected until the operation is completed and the workpiece inspected. For this reason, there has been a great need to immediately and automatically detect the lateral deviation of a band saw blade. Detection devices have been developed which provide a means for detecting and thereafter manually or automatically controlling band saw operating parameters which contribute to the cutting imprecision by varying, for example, the blade speed or feed rate, before irreparable damage is done to the workpiece.
One prior art blade deviation detection approach is to provide a detecting apparatus between the guide assembly and the workpiece which slidingly engages a side of the saw blade and detects any deflection between the exit of the guide assembly and the edge of the workpiece. Typical of such a system is the apparatus set forth in U.S Pat. Nos. 4,289,053. In this patent an endless band saw blade is formed with a deflection detection apparatus placed between the guide assembly and the edge of the workpiece. A rockable detecting arm is pivotally mounted about a hingepin with one end yieldably urged onto slidable contact with one side of the saw blade. Thus, the detecting arm moves pivotally about the hingepin in a vertical plane perpendicular to the blade travel in response to lateral deviation of the blade. The upper end of the detecting arm contacts a bell crank member hinged in movable communication with the detecting arm. This, in turn, urges a damped pushrod which cooperates with circuitry and control devices responsive to such pushrod movement to measure the lateral deviation of the band saw blade.
Another approach for measuring the lateral deviation of a band saw blade is disclosed in U.S. Pat. No. 4,355,555. This approach employs a system substantially similar to the prior art described in the preceding paragraph. In this instance, a rockable lever arm is pivotally mounted about a hinge pin proximate the lever arm midpoint. The lower end is yieldably urged in slidable contact against one side of the saw blade while the upper end is rigidly mounted to a pushrod situated at substantially a right angle. As the yieldable end detects lateral deviation, the pushrod moves in pivotal correspondence forcibly contacting a second rockable lever arm at a substantially right angle and parallel to the first rockable lever arm. The pivotal movement of a chip member, disposed atop of the second rockable arm, is sensed by circuitry designed to observe the angular displacement of the chip and, thus, lateral movement of the saw blade.
While such prior art blade deflection sensing devices are able to effectively detect lateral deflection of a band saw blade, often measuring the deviation at a fixed point may misrepresent the actual maximum deflection of the band saw blade in the cutting stretch. Turning now to FIGS. 1, 2 and 3, a prior art blade deflection sensor is schematically represented. Typically, the lateral deviation detecting apparatus is placed between the guide assemblies, generally designated 10, which define the cutting stretch. As shown, lever arm 12 is yieldably biased toward band saw blade 14 at contact tab 18 and is pivotally mounted for displacement about hingepin 16. Thus, by directly measuring the rotational motion of lever arm 12 which relatively freely pivots, the deflection or angular displacement of blade 14 from the desired line of cut is proportionately determined.
The prior art set forth above effectively detects lateral deviation when displacement occurs as viewed in FIG. 2. However, when periodic waves develop between the cutting stretch, as schematically represented in FIG. 5, the system may yield erroneous conclusions. In systems employing roller guides 20, such as U.S. Pat. No. 2,602,987 to Wells, rather than slidable guide elements, sinusoidal waves can form in the blade during the cutting operation as a result of blade sharpness differences and hardness differences. As viewed in FIG. 5, contact tab point 18 lies directly or substantially near nodal point 22 of the periodic wave in blade 14. At nodal point 22, saw blade 14 intersects the desired line of cut 24 whereby little or no displacement is sensed. Accordingly, the operator or the automatic control system is misled as to the accuracy of the cutting operation.
Moreover, the blade deflection sensing prior art discussed above does not itself promote blade guidance; they merely sense and measure it. Referring back to the prior art detecting apparatus represented in FIGS. 1-5, lever arm 12 freely displaces laterally when blade 14 deviates. Thus, arm 12 does not provide any lateral rigidity to the blade.
While the prior devices have been satisfactory for many applications, it is highly desirable to provide an assembly capable of measuring or detecting the slightest deviation from the desired line of cut while simultaneously reducing blade displacement between the cutting stretch.
Accordingly, it is an object of the present invention to provide a band saw blade deflection measuring apparatus for detecting deviations of the band saw blade from the desired line of cut which also resists lateral blade deflection during cutting.
It is another object of the present invention to provide an improved apparatus for measuring lateral deviation of band saw blades by measuring the rotational displacement of the saw blade.
It is yet another object of the present invention to provide a band saw deflection measuring apparatus which provides lateral rigidity to the measuring apparatus while retaining rotational measuring capabilities.
It is a further object of the present invention to provide an band saw apparatus measuring deflection which is durable, compact, easy to maintain, has a minimum number of components and is economical to manufacture.
The apparatus of the present invention has other objects and features of advantage which will become apparent from and are set forth in more detail in the description of the Best Mode of Carrying Out the Invention and the accompanying drawing.